1. Field of the Invention
The present invention relates to a tire mold in which a vent hole is provided in a tire molding surface which is pressed against an outer surface of an uncured tire, a manufacturing method of a pneumatic tire using the tire mold, and a pneumatic tire cured by using the tire mold.
2. Description of the Related Art
As disclosed in Japanese Unexamined Patent Publication No. 2000-37728, in a general tire mold which is used in a curing of a pneumatic tire, a lot of vent holes are provided in a tire molding surface which is pressed against an outer surface of an uncured tire, whereby air remaining between the tire molding surface and the uncured tire can be discharged out of the mold. If the discharge of the air is not appropriately carried out, a rubber short occurs in the tire molding surface due to the residual air, a deficit called a lightness (or a bare) is generated, and it may cause an appearance quality defect of the pneumatic tire.
Typically, the vent hole is set at a position at which the air tends to remain in the tire molding surface, and this position is also a position at which a reaching timing of the uncured rubber is comparatively late, however, it is impossible to arrange all the vent holes at the position mentioned above. Further, the vent holes are arranged on the assumption that the uncured rubber blocks the vent holes in such a stage that most of the air is discharged, however, the vent hole is blocked actually in such a stage that a certain degree of air has not yet discharged, and there is a case that the lightness is generated. Accordingly, the present inventor has considered that if the blocking timing of the vent hole can be further delayed, the generation of the lightness can be suppressed thereby.
Japanese Unexamined Patent Publication No. 6-143295 discloses a pneumatic tire in which a pattern portion having a predetermined surface roughness is formed in a bottom surface of a concave depression portion for forming a raised character of a side wall portion, and that a vent hole can be made unnecessary by the pattern portion. However, the technique is structured such as to decorate the raised character portion of the side wall portion like a grain woody texture or a mesh to the end, and cannot be applied to the other positions (for example, a tread surface) which do not require such a decoration, and a practical applicability is widely limited.